Interferon-gamma (IFN-gamma), also called immune interferon, is secreted by T lymphocytes when stimulated by mitogen or antigen. Wheelock, E. F. (1965), Science 149, 310; Johnson, H. M. et al. (1977), Proc. Soc. Exp. Biol. Med. 154, 138; Vilcek, J. et al. (1980) in: Biochemical Characterization of Lymphokines, eds. A. L. DeWeck et al., Academic Press, N.Y., p.323; Ennis, F. A. and Meager, A. (1982) J. Exp. Med. 154, 1279; Chang, T. W. et al. (1982) J. Immunol. 128, 585; O'Malley et al. (1982) J. Immunol. 128, 2522. Like alpha and beta interferons, IFN-gamma mediates the resistance of target cells to viral infection. It also mediates a range of immunoregulatory activities in vivo and in vitro, such as the augmentation of natural killer cell activity and tumoricidal activity. Trinchieri, G. and Santoli, D. (1978) J. Exp. Med. 147, 1314; Hansson et al., (1980) in Natural Cell-Mediated Immunity Against Tumors, ed. R. B. Herberman, Academic Press, N.Y., p. 855; Targan, S. and Stebbing, N. (1982) J. Immunol. 129, 934. In addition, IFN-gamma activates the function of macrophages by triggering proliferation, secretion of soluble factors, and expression of surface Ia and Fc receptor molecules, Steeg, P. S. et al. (1982) J. Immunol. 129, 2402; Basham, T. V. and Merigan, T. C. (1983) J. Immunol. 130, 1492.
Originally, the activation of macrophages was ascribed to a putative lymphokine, termed macrophage activation factor (MAF). However, recently it has become almost certain that IFN-gamma is identical to MAF. Some of the evidence supporting the identity of the two factors includes the following: (1) monoclonal antibodies specific for IFN-gamma neutralize all MAF activity in supernatant of activated T lymphocytes; (2) IFN-gamma and MAF activity are copurified in all isolation procedures; and (3) recombinant E. coli-derived IFN-gamma has potent MAF activity. Roberts, W. K. and Vasil, A. (1982) J. Interferon Res. 4, 519; Schreiber, R. D. et al. (1983) J. Immunol. 131, 826. Nathan, C. F. et al. (1983) J. Exp. Med. 158, 670; Le, J. et al. (1983) J. Immunol. 131, 2821.
As IFN-gamma is such an important T cell factor in host defense and in regulation of immune responses, immunologists have studied how the secretion of IFN-gamma by T lymphocytes is regulated under various conditions in vitro. Also, investigators have sought to determine whether IFN-gamma levels in the circulating blood are measurable, and if so, whether they change during active immune responses or under certain pathological conditions. Using biological assays for human interferon, Ohno and coworkers detected an increase in IFN-gamma levels in serum of patients with Behcet disease, an inflammatory disease of the eye with probable viral or autoimmune etiology. Ohno et al. (1982) Infect. Immun. 36, 202. They also reported that T lymphocytes isolated from these patients in the convalescent stage produce IFN-gamma spontaneously in cell culture. Fujii, N. et al.(1983) J. Immunol. 130, 1683. Later, Cunningham and Merigan found that peripheral blood mononuclear cells isolated from patients within three weeks after the onset of recurrent herpes labialis also secreted IFN-gamma spontaneously into culture medium. Cunningham, A. L. and Merigan, T. C. (1983) J. Immunol. 130, 2397. However, they could not detect IFN-gamma in the serum of these patients.
Functional assays for interferons, generally, are based on the ability of interferons to inhibit lysis of cultured human fibroblasts infected by viruses. See, for example Havell, E. A. and Vilcek, J. (1972) Antimicrob. Agent. Chemother. 2,476. Bioassays of this kind, however, have a number of drawbacks. Many times, they are variable and imprecise because the fibroblasts and viruses used are different. The assays normally take two to three days to run and interpretation of results (the cytopathic changes) is sometimes subjective. Moreover, the assays are not type specific, that is, they do not distinguish between the different types of interferons, IFN-alpha, IFN-beta and IFN-gamma. For these reasons, a rapid, sensitive, objective and type-specific immunochemical assay for human IFN-gamma would be highly desirable.
Monoclonal antibodies have proven useful for the characterization, identification, quantification and purification of various lymphokines. Some monoclonal antibodies to huIFN-gamma have been described in the literature. Hockeppel and De Ley describe a monoclonal antibody of the IgM class which reacts with huIFN-gamma but is unable to neutralize the antiviral activity of the lymphokine. Hockeppel, H. K. and M. De Ley (1982) Nature 296, 258-259. Rubin et al. developed a monoclonal antibody against huIFN-gamma, designated GIF-1, which neutralizes the antiviral activity of natural huIFN-gamma but not recombinant huIFN-gamma, i.e., huIFN-gamma expressed by cells harboring chimeric DNA into which the human gene for IFN-gamma has been inserted by gene-splicing techniques. Rubin, B. Y. et al. (1983) J. Immunol. 130, 1019. Finally, Novick et al. disclose monoclonal antibodies against IFN-gamma useful for affinity purification and immunoassay of huIFN-gamma. Novick, D. et al. (1983) The Embo J. 2, 1527-1530.